FoxO limits microtubule stability and is itself negatively regulated by microtubule disruption.
Bottom Line: Indeed, levels of neuronal FoxO were strongly reduced after acute pharmacological MT disruption as well as sustained genetic disruption of the neuronal cytoskeleton.This decrease was independent of the dual leucine zipper kinase-Wallenda pathway and required function of Akt kinase.We present a model wherein FoxO degradation is a component of a stabilizing, protective response to cytoskeletal insult.
Affiliation: Department of Neurosciences, Case Western Reserve University, Cleveland, OH 44106, USA.Show MeSH
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Mentions: We next investigated whether neuronal FoxO levels are also modulated by acute disruption of the MT cytoskeleton. We destabilized MTs via application of 100 µM nocodazole (Noc) using a published protocol (Massaro et al., 2009). 30-min Noc incubation disrupts dynamic MTs without visibly altering Futsch-positive MT organization (not depicted: Massaro et al., 2009) or levels of the adhesion molecule Fasciclin 2 at the NMJ (Fig. S4). Additionally, we find no changes in levels of the transcription factors Even skipped and Nkx6, Fasciclin 2, and the vesicular glutamate transporter (DVGLUT) after acute Noc treatment (Fig. 9 A and not depicted), arguing that short-term Noc incubation does not globally compromise neuronal differentiation. However, this drug treatment is sufficient to induce the Fos transcription factor (Massaro et al., 2009), suggesting activation of the JNK stress response pathway (Collins et al., 2006; Miller et al., 2009; Xiong et al., 2010). To ask whether FoxO levels are also modulated in this paradigm, we fixed tissue immediately after Noc incubation and analyzed FoxO expression. The intensity of nuclear FoxO in the CNS is reduced after Noc incubation (Fig. 9, B and C). This decrease is mirrored on Western blots (Fig. 9 D), indicating that it does not reflect altered subcellular localization. Quantification of FoxO protein levels demonstrates a twofold reduction after Noc incubation (Fig. 9 E). It is conceivable that the decrease in FoxO protein reflects regulation at the transcriptional level. However, the stability of FoxO proteins (Huang and Tindall, 2011) coupled with the rapid time course of the down-regulation argues that FoxO is actively degraded after cytoskeletal disruption.
Affiliation: Department of Neurosciences, Case Western Reserve University, Cleveland, OH 44106, USA.